1. Field of the Invention
The present invention relates to a method for producing an electrically conductive carbon film. More particularly, it relates to a method for producing an electrically conductive carbon film on a substrate by an ion beam method at a comparatively low substrate temperature.
2. Description of the Prior Art
Conventionally, an electrically conductive carbon film is produced by a pyrolysis (or thermal decomposition) method (cf. J. C. Bokros, "Chemistry and Physics of Carbon", Vol. 5, 1-118 (1969), Marcel Dekker Inc.). This method comprises heating a reaction system in an atmosphere comprising an aliphatic or aromatic hydrocarbon such as methane, ethane, propane and benzene at a temperature of 1,200.degree. to 2,200.degree. C. to decompose the hydrocarbon and depositing carbon on a surface of a substrate to form a carbon film.
The carbon film produced by the pyrolysis method has conductivity of about 0.2 S/cm, 70 S/cm, 2.times.10.sup.2 S/cm and 5.times.10.sup.2 S/cm when the substrate is heated at 600.degree. C., 1,000.degree. C., 1,200.degree. C. and 2,200.degree. C., respectively. Therefore, according to this method, it is necessary to heat the substrate at a comparatively high temperature to produce a carbon film having sufficiently large conductivity, so that kinds of the substrate are restricted to those having good heat resistance and thermal stability.
Recently, a plasma CVD (chemical vapor deposition) method has attracted more and more attention for producing an electrically conductive carbon film (cf. Y. Onuma, Y. Kato, M. Nakao and H. Matsushima, Japanese J. of Appl. Phys., 22(5), 888 (1983) and J. Shioya, H. Matsubara and S. Murakami, Synthetic Metals, 14, 113 (1986)).
The plasma CVD method comprises discharging high frequency waves in an atmosphere of the hydrocarbon as used in the pyrolysis method to plasma-polymerize it and deposit carbon on the substrate. Although the produced carbon film has a conductivity of as high as 1,000 S/cm when the substrate is heated at 1,000.degree. C., it has conductivity of 50 S/cm and 0.3 S/cm when the substrate is heated at 800.degree. C. and 600.degree. C. Such low conductivity is on the same order as achieved by the pyrolysis method.